Propylene glycol dinitrate (PGDN), commonly referred to as "Otto Fuel II", is a liquid propellant used in most torpedoes. It must be handled in all servicing shops and presents a potential health hazard to workers exposed to it. Individuals exposed to concentrations in the order of 0.1-1.0 ppm of Otto Fuel II may experience symptoms such as headache, burning sensations in the eyes and loss of motor coordination while individuals exposed to higher concentrations may experience symptoms such as changes in blood hemoglobin to metheglobin, vasodilation and liver injury. Canada has adopted a threshold Limit Value (TLV) of 0.02 ppm, although experimental evidence suggests that a more reasonable level would be about 0.1 ppm.
While various attempts have been made, there has not been developed any device capable of continuously monitoring Otto Fuel II at a concentration level of 0.02 ppm. The ideal Otto Fuel II monitor must possess a number of desirable characteristics. First, the device must be small and light so that it can be readilly moved to a site of possible contamination. It should also include an attached probe to spot check torpedoes and surfaces suspected of contamination. Second, the device must be sensitive, selective and stable. Since the monitor must be on continuously in an environment which may be contaminated with other chemicals, the detector must be highly selective for Otto Fuel II. The low TLV requires high sensitivity and stability in order to detect small amounts of Otto Fuel II on a continuous basis. Third, since Otto Fuel vapours tend not to spread rapidly, numerous detectors should be available to be positioned in likely spots of contamination. Thus, a relatively low cost is necessary to enable more of the detectors to be available. Fourth, the detector must be reliable and easy to operate since untrained individuals would use the monitor.
One known device operates on the principle that Otto Fuel II produces oxides of nitrogen when it decomposes and that the oxides react with a component in a detector tube to produce a colour change. This device does not produce an accurate reading of concentration, cannot monitor concentrations continuously, has a very slow response time, can only be used for short periods of time and has a relatively high average error. Thus, this device is obviously unsatisfactory on the basis of the criteria set forth above.
Other devices employ gas chromatography as the detecting method. While such methods have been found to be extremely sensitive, they are complex instruments to handle and, thus, use by untrained individuals is impossible. Further, these devices are rather expensive, require substantial maintenance, frequent calibration, and do not monitor on a continuous basis. Thus, while well suited for a laboratory environment, they are not practical for continuous monitoring and extensive in-field use.
Still others devices employ a Fourier Transform Infrared Spectroscopic detecting process. Their primary advantages, apart from their relatively high sensitivity, are that they can analyze air samples directly and can positively identify Otto Fuel II. However, these devices are not suitable because of cost and lack of portability.
A further device, known as the Graseby PD2-F Otto Fuel Detector, employs a sensitive electron capture detector as a sensing device and contains a argon cartridge for preconcentrating the Otto Fuel II. The preconcentrator consists of a platinum filament coated with an absorbent resin. Air is sucked over the platinum wire for a period of two seconds. The wire is then heated to desorb the Otto Fuel which is then carried by argon gas to the electron capture detector. The complete cycle takes approximately 31/2 seconds and is repeated continuously when the detector is on. Tests have shown that the detector is highly sensitive to Otto Fuel II concentrations in the range of 0.01 to 1.0 ppm. The device is portable, easy to use, has a high response time and thus appears to be ideally suited for spot checking areas of suspected contamination.
For long term monitoring, however, the latter device possesses a number of serious flaws. Firstly, it is provided with an autozero function which zeroes the detector to background air. Thus, unless the detector can be flushed out with non-contaminated air, it will eventually ignore the background concentration of Otto Fuel II. Secondly, the device cannot be used for extended periods of time without the availability of argon gas to replenish a portable bottle. Thirdly, the device is prone to interference by chlorinated compounds such as Freon 113 or trichloroethane which are used frequently in cleanup operations. Accordingly, a positive reading does not always indicate the presence of Otto Fuel II. Fourth, and among still other drawbacks, the device is relatively expensive thus precluding it from general use.